Electrical condenser



June 1950 L. E. GRIFFITHS ET AL 2,510,694

ELECTRICAL CONDENSER Filed Jan. 8,. 1948 AGENT Patented June 6, 1950 atlases U Nil f E EEECTRIIGAL CONDEFPSER LeightonE, Griifiths; ossining and Johannes-N." Hiensch,;Larchm9nt; N.,Y., assignors' towlthilips: Laboratories, .Inc., Irvington on Hudson, Y.

Application January- 8, 1945; ser eant. 139W 4. Claims.

This invention relates: to; electrical 1 condensers:

and: particularly to adiustable -capacitycon-.

densers comprising a glurality of interfitting tunection with s-uchadjustable; condensers. Con-- densersvoemprising electrodes: in, the; form of-o interfitting; concentric, metal cupssecured; to: a commen base arevpresentlyknown in the artas will r be seen by reference .toTU; S. Patent-Nor 2,-161A19 issued-June 63.1939; which patent discloses amethod; oi-.-manufacturine; the:- lectrodes of the condenser; from--'a,-singles; piece: of ma,

terial in a single operation by? means ota cold squirting process.

Condensers of this typeha've also been-= made by machining theelectrode from a single block,

or metal or by die casting thametalin the-form of an integral assembly.

Condensers made-by cold. squirting? the metal thereof have-beeniound tobe-of comparatively high cost; When it attempted'to makethe concentric cup; electrodes-by machine forming a solid blochoithe metal, it isfound. that theconcentric walls of the cups.;must. be made-com paratively thick in order to: prevent tearing;- of.- the metal by the; cutting tool'and. to prevent distortion; oi -T; the cup-shaped; electrodes due to the" localized heating; occurring; during the, cut-h ting; zVhile-the-die-castingmethod isthe-cheap est methodi inattem-ptstut-die cast, theelectrodel, it" has been: found; that the walls: must beymade of; si-zbstantial thickness-as, otherwise: they tear when; the die removed; These unsatisfactoryconditions prevailigarticularly when smallsize condensers are'tobe madefi;

It: an object; oitheinvention: to pmY-ide, a,

novel condenser; which;obviates: the-ior%oing clifliculties in. the; manufacture thereof Another object of" the invention: is.- to;: provide adjustable condensers comprising concentric in. terleaved cup-shaped electrodes characterized bya low: costtand a high-- degreeof uniiormity. v

A further object: of the-invention is zto provide novel adjustableroondensen whiohdslnon microphonic andlwhichg is; stable when subjected.- tochanges in temperature and, hu-.

midity' These andsfurtheraobjects oi the invention will appear as thespecificationpmgresses.

According torthe-presentinvention we: pro-ll (Cl. HST-4:115)

2 v-ide: an; adjustable;- cqndfinsert havin concentric interleaved cup. hoped electrodes constituted by a-formed body-o a pulverulent-nommetallic electricallvconclucting;material such as graphite and produce the said. electrodesgby machining a blocl;

of the said material tQfQIlnflQilCGl'lllIiG; tubular portions integ ally; onnected; to: a baseportion.

In-v he; preferr d arran ement? or, the invention, the walls of; the; concentric; cues are provided: with one-or; more; metal Pia-tings; whereby the strength ofi'the; walls thereof; is: increased manya fold and; at I tI-IC:S&II1E; time the electrode is made, resistant. to; humidity: changes and; the; effective electrical; resistance thereof?v event at high fre 5 quenciesisreduccd tQas-ma-llvalue;

Becausecf thew'pulverul'ent quality ef'the material oi; the body;- from w-hiehare formed the electrodes, the: body; may be readily machinedwithout tearing -01- dis-tortion thereof to produce electrodes having umiormwall thickness of theorder 05.008 inc-h;- Furthermore; because of theinherent propertiesoil the pulverulent material, the; electrode is ri-ggid and a condenser, so formed islnon-omierophonic. A: formed body ofgraphite- 8wbeenfouniparticularlysuitable for the put poses-- of the invention; More particularly, a formed bod-y of granhitenotonly-v exhibits a low temperature-coefficient of expansion thereby bringing -about a condenser of great temperature stability, butalso the graphite serves as a lubricant; fol: the machining tool whereby no signifi cant heatingof; theytoel and of, the graphite ocours and distortions; oftheresultant electrodefrom thiscause are prevented. Particularly suit-'- ablefor thepurpose Offbhfi invention-are formed-- common base portion l5. The cup-shaped portions ii and the cup-shaped portions M are so spaced so as to freely interfit without short circuiting upon axial movement of the electrode l3 relative to the electrode It. Each of the electrodes I and i3 is constituted by a pulverulent non-metallic electrically conducting material, preferably graphite, conforming to the above noted characteristics. In accordance with the preferred embodiment of the invention, each electrode is provided with a copper plating and a superimposed silver plating. The composite plating on electrode i0 is shown at it and the plating on electrode is is shown at IT. The copper plating is preferably from .0005 to .001 inch thick although it is obvious that thicker films may be applied particularly in those instances when a condenser having an extremely 4 phate (Na4P2Om10H2Q) 26.5 ounces and sodium chloride (NaCl) 3.8 ounces. Potassium hydroxide is added to the solution to adjust its pH value to approximately 8.2. The solution is maintained at a temperature of approximately 130 F. and by applying a current density of approximately amperes per square foot for approximately 30 minutes a copper plating of approximately .0005 inch thick is formed over the electrode surfaces. The subsequent silver plating of the so processed electrodes takes place in an aqueous solution consisting per gallon of solution of 3 ounces of silver cyanide, 6 ounces of potassium cyanide, 6 ounces of potassium carbonate, and .02 ounce of carbon disulphide. The solution is maintained at a temperature of 90 F. and the electroplating high current carrying capacity is desired or where greatly increased strength is required. However, the plating should not be too thick or otherwise the low temperature coefficient of capacity normally existing because of the low temperature coefiioient of expansion of the underlying graphite is impaired. The superimposed silver plating is approximately .0001 inch thick and this thickness we have found is sufiicient to ensure a permanently clean surface, prevent corrosion of the condenser and to provide a low resistance current conducting coating to which electrical connection to the electrodes may be made.

A metal lug it! provided with a silver coating i9 is force fitted within a peripheral recess 20 of the said stator electrode l0. For coaxially aligning the electrodes l0 and it, there is provided a tubular shaped ceramic member 2i which is press fitted into a central opening 22 of the stator electrode 40 and which forms a sliding fit Within the cavity or the inner of the cup-shaped walls M of the rotor electrode l3. A flanged cap member 24 providedwith an outer silver plating 25 is tight fitted to the lower end of the said ceramic sleeve 2i. For moving the electrodes l0 and i3 relative to each other, there is provided a threaded spindle 26 which is attached at one end to the flanged cap 24 by means of a threaded nut 2'? and engages corresponding threads in the aperture 28 of the rotor electrode l3. A look nut 29 secured to an axially extending portion 30 of the rotor is secures the rotor against inadvertent rotation along the threaded spindle 26.

Well known procedures and plating solutions may be used for applying the copper and silver electroplatings i0 and H to the electrodes !0 and it. However, we have found the following procedure and plating solutions to be particularly efiective in view of the'enhanced throwing power realized which provides uniform and continuous platings even within the deep recesses formed by the concentric cup-shaped walls of the electrodes. v

For applying the copper plating, the electrodes Ill and I3 are first given a strike plating in an electroplating solution comprising 1 gallon of water, 2 /2 ounces of copper cyanide, 3 ounces of sodium cyanide and 1 ounce of caustic soda. A satisfactory coating is formed at a current density of 2-5 amperes per square foot applied for about one minute. After thoroughly rinsing, the electrodes are given an intermediary acid dip, for example, in 1% sulphuric acid and thereafter the copper plating is applied. A suitable solution for the copper plating comprises per gallon of aqueousf'solution, copper sulphate (CuSO45I-I2O) 26.5 ounces, sodium pyrophostakes place at a current density of 10 to 15 amperes per square foot for about 5 minutes. The electrodes are then thoroughly rinsed and after drying preferably in a hot air column, the electrodes are assembled to form the condenser shown.

One or more strike platings may be applied to the electrodes prior to the aforementioned silver plating to facilitate the deposition thereof. A suitable aqueous solution for this purpose may comprise per gallon, 10 ounces of sodium cyanide, 8 ounces of copper cyanide, /2 ounce of silver cyanide. At a plating temperature of F. and a current density of 20 amperes per square foot a strike coating is formed in about one minute.

While we have described our invention by means of specific examples and in a specific embodiment, we do not wish to be limited thereto for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

What we claim is:

1. An electrical condenser comprising a first electrode having a base portion and a plurality of concentric tubular wall portions integrally extending from said base portion, and a second electrode having a base portion and a plurality of concentric tubular wall portions extending from said second base portion, said first and said second tubular wall portions being arranged in spaced inter-fitting relationship, said base portions and said wall portions being constituted of a formed body of a graphite, and low electrical resistance metal layers forming electroplatings on said base portions and said wall portions.

2. An electrical condenser comprising a first electrode having a base portion and a plurality of concentric tubular wall portions integrally extending from said base portion, a second electrode having a base portion and a plurality of concentric tubular wall portions extending from said second base portion, said base portions and said wall portions being constituted of a formed body of graphite, copper layers forming electroplatings on said base portions and said tubular wall portions, silver layers superimposed on said copper layers, and means securing said first and second electrodes in interfitting spaced relationship.

3. A condenser comprising a supporting base, a plurality of tubular cup-shaped graphite members of different diameters all having their bases in electrical connection and being provided with a metallic covering to exclude moisture absorption by the graphite, said cups being nested in one another to form a single first electrode structure, a series of similar cup-shaped tubular members of graphite having a common base connection and being plated to exclude moisture absorption by the graphite forming a second electrode structure, the tubular cup-shaped members of the second electrode having successive diameters at which the first and second electrodes are interleaved.

4. A condenser comprising an insulating supporting base, a plurality of tubular cup-shaped graphite members of different diameters having a common base providing an electrical connection between the several members, a composite metal layer over the graphite to exclude moisture absorption by the graphite, comprising a first layer of copper over the graphite and a second layer of silver over the copper, said cups being nested in one another to form a single first electrode structure, a series of similar cup-shaped tubular graphite members having a common base, which form a second electrode structure, a composite metal layer over the graphite of the second electrode comprising a first layer of copper over the graphite and a second layer of silver over the copper, the tubular cup-shaped members of the second electrode having successive diameters at which the first and second electrodes are interleaved.

LEIGHTON E. GRIFFITHS. JOHANNES N. HIENSCI-I.

6 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,150,895 Sloan Aug. 24, 1915 1,718,783 Herman June 25, 1929 2,031,846 Muth Feb. 25, 1936 2,165,738 Van Hoffen July 11, 1939 2,225,770 Dorn Dec. 24, 1940 FOREIGN PATENTS Number Country Date 416,457 Great Britain Sept. 14, 1934 558,281 Great Britain Dec. 29, 1943 20 tion M-BOOOA, National Carbon 00., Inc.; pages 2 and 19. 

